Tin-based plain bearing alloys have been known for decades as white metals, for example, and comprise antimony and copper as principal alloying elements, the alloy being supplemented by further elements.
The plain bearing alloy is in this respect regularly cast onto a supporting structure, e.g. made of steel, for example in the form of a bearing supporting shell. The plain bearing alloy should have a good embedding capacity for dirt particles and a good adaptability to the elements which slide on one another, for example a rotating shaft. The tin-based sliding metal alloys have these properties, but are limited in terms of their load-bearing capacity. Since the demands made in respect of the durability of plain bearing alloys are on the increase, plain bearing alloys which can be subjected to a higher level of loading, for example those based on aluminum-tin, have therefore increasingly been used. However, these plain bearing alloys do not have the advantageous properties in respect of the embedding capacity and adaptability which the tin-based plain bearing alloys afford. Numerous tests have therefore been carried out to improve tin-based plain bearing alloys with respect to the load-bearing capacity, i.e. in particular with respect to their hardness and fatigue strength.
It is known from DE 28 18 099 C2 to provide a tin-based white metal containing the alloying elements antimony, copper and cadmium and also, as grain-refining elements, chromium and cobalt additionally with 0.02 to 0.08% by weight boron and 0.1 to 0.2% by weight zinc. A combined action of boron and zinc, together with cobalt and chromium, achieves a significant improvement in the strength property. The impairment in the bond to the steel supporting shell which arises as a result of zinc is nullified further by the addition of boron.
GB 2,146,354 A discloses a tin-based plain bearing alloy comprising the principal alloying elements antimony and copper, in which the strength is to be increased by grain refinement on account of the addition of titanium in a proportion of 0.005 to 0.5% by weight.
SU 1 560 596 A1 discloses a tin-based plain bearing alloy comprising, as principal alloying elements, 7 to 8% by weight copper, 10 to 12% by weight antimony and to 20% zinc, remainder tin. The alloy has an increased durability and wear resistance, but can be applied to a steel substrate only by means of arc spraying. If this alloy were to be applied by casting, it would not be usable as a plain bearing alloy owing to an excessively low toughness.
A further demand which is made in respect of the plain bearing alloys used is that of keeping said alloys free from pollutive alloying constituents, in order to ensure ecologically compatible plain bearing alloys (white metal alloys). It has not been possible to date, however, to create such plain bearing alloys which satisfy higher demands in terms of strength. Given higher demands in respect of the load-bearing capacity and in respect of the wear resistance, it is therefore often the case that aluminum-based bearing metals continue to be used, even though the use of these bearing metals means that it is necessary to dispense with the outstanding emergency running properties of tin-based bearing metal alloys.
WO 2009/108975 A1 discloses a white metal comprising 4 to 30% by weight antimony and 1 to 10% by weight copper. The alloy in this case should furthermore comprise an element selected from the group of elements consisting of cobalt, manganese, scandium and germanium, with a total concentration of between 0.2 and 2.6% by weight, and also at least one element selected from the group of elements consisting of magnesium, nickel, zirconium and titanium, with a total concentration of between 0.05 and 1.7% by weight, the sum proportion of antimony and copper, given an antimony content which corresponds at least to three times the copper content, being at most 35% by weight. The plain bearing alloy can contain an addition of 0.6 to 1.8% by weight, preferably 0.7 to 0.9% by weight, zinc. Zinc serves, through the formation of additional crystallization nuclei, for refining the copper-tin and tin-antimony phases. This prevents the growth of these phases to a harmful size. The lower limit of 0.6% by weight zinc arises from the fact that a smaller addition no longer generates a positive effect, whereas the upper limit arises from the fact that, above 1% by weight, the zinc is no longer dissolved in the tin solid solution, and a low-melting eutectic phase is formed, at a Tm of approximately 200° C., between tin and zinc, this lowering the high-temperature strength and also the corrosion resistance.